I've noticed over the years that a lot of anime series just place the eyes right on top of the hair. Sometimes it's done artistically and actually makes the series more enjoyable, but at other times it appears to just be down right lazy.

Exhibit A - The Floater:
Sorry, but I kept wanting to try to peel off Akunes eyes that entire episode of Medaka Box!

In the first example, which is fairly common, it is so you can see eye expressions. In Ano Natsu, whenever a character with glasses was shown from the side, the arms of the glasses would have gaps so you could see the character's eyes.

They make the floating eyes because it's easier to draw the eyes alone rather than draw everything together when its moving. If you own some key frames (genga) then you can see how everything is drawn and broken down.